pin python version to 3.7 (#461)

Author: Roberto Sora

.github/workflows/test.yaml

@@ -67,7 +67,7 @@ jobs:
       - name: Install Python
         uses: actions/setup-python@v1
         with:
-          python-version: '3.x'
+          python-version: '3.7'
           architecture: 'x64'
 
       - name: Run integration tests